Mendel's "factors" are __, which are located along chromosomes.
Using improved techniques of microscopy, cytologists worked out the process of ___ in 1877 and __ in the 1890s.
--> __ and __ converged when biologists began to see parallels between the behavior of __ and the behavior of Mendel's proposed ___ during sexual life cycles:
-----------__ and __ are both present in pairs in __ cells; __ separate and __ segregate during the process of meiosis; and __ restores the paired conditions for both chromosomes and genes.
Around 1902, Walter S. Sutton, Theodor Boveri, and others independently noted these parallels, and the ___ began to take form.
chromosome theory of inheritance
What is the chromosome theory of inheritance?
according to this theory, Mendelian genes have specific loci (positions) along chromosomes, and it is the chromosomes that undergo segregation and independent assortment
Behavior of __ during meiosis can account for the segregation of the __ at each genetic __ to different __.
The behavior of _ can account for the independent assortment of the __for two or more genes located on different chromosomes.
Thomas Hunt Morgan, for his experiment, used a __.
-- prolific breeders (hundreds of offspring/ new generation bred every two weeks)
--only has four pairs of chromosomes, which are easily distinguishable with a light microscope (3 pairs of autosomes/ one pair of sex) (females - XX) (males- XY)
True or False: Morgan got no results for two years, but was rewarded with the discovery of a single male fly with white eyes instead of the usual red.
The phenotype for a character most commonly observed in natural populations, such as red eyes in Drosophila, is called a __.
Traits that are alternatives to the wild type, like white eyes of Drosophila, are called __ because they are due to alleles assumed to have originated as changes, or mutations in the wild type allele.
Morgan invented notation for symbolizing alleles in fruit flies:
- For a given character in flies, the gene takes its symbol from the first __ discovered.
---- The allele for white eyes is symbolized by __, and the wild type trait is __, for red eyes.
mutant (non wild-type)
What were Morgan's results when he mated his white-eyed male fly with a red-eyed female?
All F1 had red eyes (wild-type allele is dominant)
F1 individuals had 3:1 phenotypic ratio oamong the F2 offspring, with an additional result:
-- white-eyed trait only in males
-- all F2 females had red eyes, while half the males had white, and half had red
--He concluded that somehow a fly's eye color was linked to its sex
The correlation between the trait of white eye color and the male sex of the afffected F2 flies suggested to Morgan that the gene iinvolved in his white-eyed mutant was located exclusively on the __, with no corresponding allele present on the __.
- For a mlae, a single copy of the __ would confer white eyes; since a male has only one __ chromosome, there can be no __ present to offset the __ allele.
- On the other hand, a female could have white eyes only if both her __ chromosomes carried the recessive __. THis was impossible for the F2 females because the F1 fathers had red eyes.
- His findings of the correlation between a particular trait and an individual's sex provided support for the __: namely, that a specific gene is carried on a specific chromosome.
- In addition, his work indicated that genes located on a __ chromosome exhibit unique inheritance patterns.
wild-type allele (w+)
mutant allele (w)
chromosome theory of inheritance
Chapter 15: The Chromosomal Basis of Inheritance (1)